I'm happy to hear this. The problem sort-of is: Do you have the kind of measurement equipment to facilitate that kind of development? In order to e.g. test the VCO/PLL / Transmit code, you would have to have something like a spectrum analyzer or a scope that can go up to at least the GSM900, preferrably up into 1800/1900 MHz.
If you want to test the receive side, something like a GSM signal generator (HP 8922, Racal 6103, R&S CMD 55) would be great, as they can transmit a well-known bit pattern (all-1, all-0, 101010101010 and the like) on a configured ARFCN, then configure the RF Transceiver (MT61400 and you can watch the analog baseband signal on an oscilloscope and determine if it mathes the expected singal.
I have access to such equipment. I have access to Agilent Spectrum Analyzer E4405B (9kHz - 13.2GHz) and Rohde&Schwarz CMU200 (Universal Radio Communication Tester, it also has spectrum analyzer). In this case there're no obstacles to start, only matter of time available for this project.
BR, Marcin